Question

Solve the system -4x+8y=20 2x+2y=-30

Answer 1

Answer:

 {x,y} = {-35/3,-10/3}

Step-by-step explanation:

 -4x+8y=20;2x+2-30  

System of Linear Equations entered :

  [1] -4x + 8y = 20

  [2] 2x + 2y = -30

Solve by Substitution :

// Solve equation [2] for the variable  y 

[2] 2y = -2x - 30

[2] y = -x - 15

// Plug this in for variable  y  in equation [1]

  [1] -4x + 8•(-x -15) = 20

  [1] -12x = 140

// Solve equation [1] for the variable  x 

  [1] 12x = - 140 

  [1] x = - 35/3 

// By now we know this much :

  x = -35/3

  y = -x-15

// Use the  x  value to solve for  y 

  y = -(-35/3)-15 = -10/3 

Solution :

 {x,y} = {-35/3,-10/3} 

Answer 2

Answer:

x = -13 and y = -4

Step-by-step explanation:

-4x + 8y = 20 ................... eqn 1

2x + 2y = -30 ................... eqn 2

Step 1: Multiply eqn 1 by 2 and eqn 2 by 4

(-4x + 8y = 20) × 2

(2x + 2y = -30) × 4

we will have

-8x + 16y = 40 ....................eqn 3

8x + 4y = - 120 .................. eqn 4

Step 2: Add eqn 3 and 4 together

20y = - 80

Step 3: divide all through by 20

y = -80/20

y = -4

Step 4: Substitute -4 for y in eqn 1

-4x + 8(-4) = 20

-4x - 32 = 20

-4x = 20 + 32

-4x = 52

Step 5: Divide both sides by -4

x = 52/-4

x = -13